Hydrologic Modeling with SSARR and HEC-HMS

Crane Johnson, PEHydraulic EngineerUS Army Corps of EngineersAlaska District

Streamflow Synthesis and Reservoir Regulation Model

Streamflow Synthesis and Reservoir Regulation (SSARR) Model was developed to provide mathematical hydrologic simulations for systems analysis as required for the planning, design, and

operation of water control works.

Consists of two Sub-models:

•Watershed Model

•River System and Regulation Model

SSARR

•Developed in the 1960’s by the Corp of Engineers Northwest Division, last major update 1991

•Still used today to model un-regulated Columbia and Snake River flows

•Written in FORTRAN 77, DOS Operating System

•Used by the Alaska District as an Operational model to forecast flood flows for the Chena River Lakes Project.

SSARR

FAIRBANKS FLOOD OF 1967

Photo courtesy of VF Addendum, 89-12-83, Archives,

University of Alaska Fairbanks.

•Displaced 7,000 People

•$80 Million in Damages

•Inspired Congress to pass the National Flood Insurance Program (NFIP)

•6.20” of rain in Fairbanks (August 1967)

•74,000 cfs, Downtown Fairbanks

Chena River Lakes Project

1958 – Project Authorized

1968 – Project Re-Authorized

1970 – Design Begins

1973 – Tanana Levee Construction Begins

1975 – Moose Creek Dam Construction Begins

1979 – Moose Creek Dam Operational

1981 – Project Test Fill

1988 – Construction of All Project Elements Complete

CHENA RIVER LAKES PROJECT

OPERATIONAL SCHEMATIC

ALASKA DISTRICT

DAM SPECIFICATIONS

• TYPE: Zoned Earth Fill• ELEVATION: 528.7 Feet MSL (max @ top)• HEIGHT ABOVE STREAM BED: 50 feet• LENGTH: 40,200 feet• WIDTH AT TOP: 24 feet• VOLUME OF FILL: 6,231,000 cubic yards• STORAGE CAPACITY: 224,000 acre-feet

@ 525 feet elevation @ control works

ALASKA DISTRICT

DISCHARGE FACILITY

Type: Concrete gravity control works

Gates: 4 steel, vertical lift

Gate Openings: 18 ft high X 25 ft wide

Fishways: 2 each, 5 ft wide X 18 ft high

Fish Ladder: Vertical slot width = 0.75 feet

Maximum discharge = 26 cfs

CHENA FLOODWAY

• Length: 27,000 ft (Chena River to Highway Bridges)

• Minimum Width of cleared flow channel: 1,100 feet

• Maximum Width of cleared flow channel: 4,200 feet

• Channel-peak design outflow: 160,000 cubic feet per second

Floodway Sill:

• Type: Sharp-Crested Weir

• Material: Sheet piling with

rolled concrete stilling basin

• Crest Elevation: 506.65 feet (MSL)

• Crest Length: 2,000 feet

• Purpose: Prevent Tanana River floods

from entering Chena River.

ALASKA DISTRICT

HIGH WATER EVENTS

• 20 High Water Events from 1981 through 2008

• The 3 Largest Events to Date:

Peak Peak Peak Gate

Floodway Flow @ Flow @ Closure

Elevation Outlet Works Fairbanks Duration

Dates Feet (MSL) (CFS) (CFS) (DAYS)

May-June 1992 507.6 8,200 10,500 18

May 1991 503.0 8,300 11,350 11

May-June 1985 505.3 8,250 8,950 12

ALASKA DISTRICT

CHENA RIVER LAKES FLOOD CONTROL PROJECT

ALASKA DISTRICT

CHENA RIVER LAKES FLOOD CONTROL PROJECT

Chena River Lakes Project SSARR Model

•Lumped parameter model with 4 sub-basins

•Each sub-basin includes elevation bands

•Moose Creek Dam and Reservoir Included

•Two sets of operating rules

•Maximum release

•Minimum release (upstream fish migration)

ALASKA DISTRICT

CHENA BASIN SSARR MODEL

Watershed Sub-Model

Basin weighted averages (with elevation zone adjustments) for:

Air Temp

Precipitation

Interception – Bucket Model

Evapotranspiration – Thornwaite Method

(adjusted for elevation, season and snowcover)

Snowmelt – Temperature Index Method

Runoff – Empirical relationship SMI vs. Runoff%

(varies with rainfall rate)

Four runoff zones are routed to the Stream

(routing through series of small lakes)

ALASKA DISTRICT

CHENA BASIN SSARR MODEL

River System and Regulation Sub-Model

•Reservoir Routing – Continuity of storage equation

•Stream Routing – Cascade of reservoirs

Time of Storage decreases with increasing Q

Ts= KTS

Qn

ALASKA DISTRICT

CHENA BASIN SSARR MODEL

ALASKA DISTRICT

Strengths:

•Includes both watershed and river routing processes

•Includes reservoirs and regulation operating rules

•Long history of use in Interior Alaska

•Empirically based methods with lots of calibration data

Weaknesses:

•Difficult user interface

•Limited graphical output capabilities

•Empirically based model – limited hydrologic methods available

•No automatic adjustment of initial conditions available

CHENA BASIN SSARR MODEL

Hydrologic Engineering Center -

Hydrologic Modeling System

(formerly HEC-1)

HEC-HMS

•HEC “NexGen” Project Begins 1990 (RAS, HMS, FDA)

First HEC-HMS Release April 1998•Version 1.1 Released April 1999•Current Version 3.4

ALASKA DISTRICT

HEC-HMS

HEC-HMS HEC-1 Purpose of HEC-HMS

– Improved User Interface, Graphics, and Reporting

– Improved Hydrologic Computations– Integration of Related Hydrologic Capabilities

Importance of HEC-HMS– Foundation for Future Hydrologic Software– Replacement for HEC-1 (Advanced Version)

ALASKA DISTRICT

HEC-HMS

– Ease of use– Projects divided into three components– User can run projects with different parameters

instead of creating new projects – Hydrologic data stored as DSS files– Capable of handling NEXRAD-rainfall data and

gridded precipitation– Quasi-distributed model

IMPROVEMENTS OVER HEC-1

ALASKA DISTRICT

HEC-HMS

3 Major Hydrologic

Processes for each Basin

•Losses (10 methods)

•Transformation to runoff (7 methods)

•Transformation to baseflow (5 methods)

ALASKA DISTRICT

HEC-HMS

Hydraulic Methods Kinematic Wave MethodMuskingum-Cunge Method

Hydrologic MethodsMuskingum MethodStorage Method (Modified Puls)Lag Method

Six Streamflow Routing Methods

ALASKA DISTRICT

EKLUTNA HEC-HMS MODEL

ALASKA DISTRICT

CHENA RIVER LAKES PROJECT

SSARR HEC-HMSAdvantages

ALASKA DISTRICT

QUESTIONS????